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PubMed · 8164590

The head-scatter factor for small field sizes.

T C Zhu·B E Bjärngard
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Abstract

The head-scatter factors H were examined for four different linear accelerators and were found to be similar at field sizes larger than 3 x 3 cm2. Sharply reduced values for small collimator openings were observed for all the accelerators. It is concluded that the head-scatter (or collimator-scatter) factor has two major components. Scatter of photons in various structures in the beam path, especially the flattening filter, causes a slow (about 10%) increase with increased collimator opening. Insertion of a built-in wedge may double this number. When the collimators are closed, they ultimately block photons from the periphery of the source. This may cause a considerable reduction of the primary photon fluence and typically affects fields smaller than 3 x 3 cm2. The effect can be used to estimate the source size, with results that correlate with the design of the bending magnet.

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Biophysical PhenomenaBiophysicsHumansModels, StructuralModels, TheoreticalParticle AcceleratorsPhotonsRadiotherapy Planning, Computer-AssistedRadiotherapy, High-EnergyScattering, RadiationJournal Article

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T C Zhu, B E Bjärngard. 1994. The head-scatter factor for small field sizes.. https://doi.org/10.1118/1.597256

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